Question

The following are three pathways that are involved in cellular respiration. i. Glycolysis i. Electron transport chain ii. Tricarboxylic acid cycle Which of the above pathways are catabolic reactions? Explain the reason, why they are catabolic or why they are not catabolic pathway?

Answer 1

ANSWER:

Of mentioned pathways, the Gycolysis and Electron transport chain can be considered as Catabolic reactions.

The Tricarboxylic acid cycle (TCA cycle) is an amphibolic pathway

Reason:

1) Catabolic reactions (Gycolysis and Electron transport chain)

Catabolism is the part of the metabolism responsible for breaking, degradation or decomposition of complex molecules down into smaller molecules. The other part of the metabolism, anabolism, builds simple molecules into more complex ones. During the catabolism, energy is released from the bonds of the large molecules being broken down, and this can be used to form macroergic molecules.

Glycolysis is a universal catabolic pathway that breaks down the glucose into pyruvates through a sequence of enzyme catalysed reactions, which can be used for later mechanism (Krebs cycle) to produce high-energy molecules ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide). Its primary function is to provide energy and intermediates for other metabolic pathways. Energy that is released from catabolism will store as ATP (adenosine triphosphate) within the cell.

The electron transport chain (ETC) is a also catabolic process in which the NADH and [FADH2] produced during glycolysis, β-oxidation, and other catabolic processes are oxidized thus releasing energy in the form of ATP.

As a note; Few important catabolic reactions occurring in our body are glycolysis, electron transport chain, lipolysis, degradation of ketone bodies, proteins or amino acids.

2) Amphibolic reactions (Tricarboxylic acid cycle)

An amphibolic pathway is the metabolic process which have a character of both breaks down (catabolic) and break up (anabolic) reactions.

The TCA cycle is amphibolic since it functions to provide energy in addition to chemical intermediates for the synthesis of cell material (provides the number of intermediates for the anabolic pathway). Thereby, in this process, both catabolism and anabolism occurs.

During the TCA Cycle, energy is both consumed and produced. The acetyl co-enzyme A (coA) is converted to CO2 and H2O, but during this process electrons are transfered to NADH and FADH2. These electron go through the electron transport chain to make ATP (production and storage of energy). And during the conversion process, the ATP is used to convert the intermediates (Succinyl CoA to Succinic acid).